Tonnes of microplastic are soaring into the atmosphere from roads, oceans and fields

A new study has shown that large amounts of microplastic are floating into the atmosphere from roadways, oceans and farm fields. Once there, it can be carried by winds to the most remote places on Earth. 

Airborne microplastic takes many forms and comes from many different sources, according to the researchers, but a key contributor is discarded plastic waste. Since plastic biodegrades very slowly, it just fragments into smaller pieces that can be carried by air currents.  A significant amount of these fragments come from synthetic textile fibres. 

"It can be either as really small fibres, films, what we call particles or even microbeads," Canadian researcher Janice Brahney told Quirks & Quarks host Bob McDonald.

"So very, very tiny particles, much smaller than what you could see with the naked eye."

Brahney, an associate professor of watershed sciences at Utah State University, worked with colleagues to investigate the sources of airborne plastic and how the plastic entered the atmosphere. Their study was published in the Proceedings of the National Academy of Sciences.

The team first identified how plastic particles find their way into the atmosphere to begin with. 

Their study focused on sources and samples from the Western United States. Brahney used available information on sources and amounts of microplastics, as well as samples the team collected from 11 remote wilderness locations, to understand how microplastic is entering the atmosphere.

She and her team found three main ways this was happening.

"Highways and roads were really the most important variable for moving plastic into the atmosphere. This is because plastics are now basically everywhere, including on roads," said Brahney.

"When a car passes over a road, it generates that energy that can move plastics high into the atmosphere. Imagine a car driving on a dirt road. You can see that plume of dust coming up after it. Within all that dust is also microplastic."

The road to microplastic

Even though many roads and highways are in urban areas, cities themselves are not a main source of atmospheric microplastic. Brahney suggested this may be because cities have so many places to catch and trap microplastics before they reach the atmosphere.

Another way microplastic ends up in the atmosphere is from the movement of ocean waves.

"Because microplastics tend to be a lot less dense than water, they're floating on the surface," said Brahney. "As the waves are churning and bubbles are bursting on the surface of the ocean, that has the capacity to emit these tiny particles into the atmosphere where they can then be transported." 

One thing that surprised Brahney and her colleagues was that their work showed more atmospheric microplastic makes its way from oceans to land, rather than the other way round. That's because the oceans hold more of what is called "legacy pollution" — decades-old particles that are now being picked up from the sea by winds, and subsequently deposited on land.

The third way microplastic particles ended up in the atmosphere was due to agriculture.

The researchers identified two major sources of plastic in agricultural soils. First, biosolids from wastewater treatment plants are used as fertilizer, and include significant amounts of plastic. Second, in recent years plastic mulch has been used in significant amounts in agriculture and can enter soils. 

"Over time, those plastics break down and end up being incorporated into the soil," Brahney said. "We think that agricultural soils will have really high concentrations of microplastics compared to wild land soils. Then when the fields are fallow or when they're being tilled, there's the potential to produce dust from those activities."

We end up inhaling microplastic

According to Brahney's models, plastic particles can stay in the atmosphere anywhere from a few hours to more than six days.

"That's certainly long enough for plastics to travel in between continents and reach every corner of the globe," she said.

The impact of microplastic in the atmosphere is unclear to the researchers at this point. Brahney suggested the particles could influence atmospheric chemistry, including cloud formation, and therefore have some impact on weather. They could also affect the balance of solar radiation that we need for heat and energy.

It is hard to quantify the amount of microplastic in the air, but Brahney has generated an estimate based on her area of study. 

"Above the Western United States, at any given time, there's about a thousand tonnes of microplastics in the air. And if we extrapolate that across the entire United States, we estimated about 22,000 tonnes per year. It's also estimated that we consume and inhale about a credit card's worth of microplastic every single week." 

Written and produced by Mark Crawley.